Controlling Equine Herpesvirus

Take steps to protect your horse from equine herpesvirus. By Laurie Bonner for EQUUS magazine.

Vaccines against herpesvirus are useful but offer limited protection. |

It’s impossible to protect your horse from equine herpesviruses (EHVs) entirely. But some simple measures can minimize the chances that he’ll get an infectious dose of EHV-1 and EHV-4, the types most likely to cause trouble with the flu-like Rhinopneumonitis (rhino) and late-term abortions. Consider these precautions:

Vaccinate. Because of the nature of the herpesviruses, the vaccines against EHV-1 and EHV-4 offer only limited and temporary protection. Nonetheless they are often worthwhile, says George Allen, PhD, a researcher from the University of Kentucky. “In young horses who have never been exposed to the virus, the vaccine causes the signs [of a subsequent infection] to be less severe. In older horses, the main benefit of vaccination is to prevent the virus from spreading to other horses.” In addition, it’s wise to inoculate pregnant mares against EHV-1. Although the vaccines cannot help a mare who may experience a reactivation of a latent strain during pregnancy, it will prevent her from spreading the virus to other members of her herd and triggering an abortion storm.

Isolate newcomers for about three weeks before introducing them into established herds. Herpesviruses are readily spread when a new horse carrying a different strain of the virus is brought into a group, especially since the stresses of travel and “settling in” can activate a latent virus. If possible, isolate newcomers for two to three weeks, which will allow any active viral shedding to subside, before turning them out with your existing herd. Isolation is also a good strategy if you’ve already had an outbreak. Horses who have been sick with a herpesviruses usually continue to shed the organisms for only a week or two after the infection subsides, so three weeks is the usual quarantine period recommended after a rhinopneumonitis outbreak.

Remove aborted fetuses promptly. The tissues and fluids of a fetus aborted due to EHV-1 are highly infectious, and the virus can easily be spread to curious nosers who might come in contact with it. If you’re unsure why a mare aborted, then it’s safest to assume that the fetus might be harboring the virus. Place all tissues in sealed plastic bag and save it for your veterinarian to inspect, then clean and disinfect the site where you found it. If it was in the field, hose down the area and apply a chemical disinfectant; even better, remove all other horses from the field, if possible, for the weeks it would take for the viruses to die out. If it was in a foaling stall, remove all the bedding and disinfect the walls and floor before placing another horse there. Don’t forget to thoroughly wash your hands, clothes and any tools you used as well as the mare herself.

Wash thoroughly after handling sick horses. Herpesviruses usually pass from horse to horse, but contagion can also be carried on people’s hands, clothing or tools. Since horses can shed herpesviruses without showing any signs of illness, it’s wise to always practice simple cleanliness–washing with soap especially after doing anything that brings you in contact with the horse’s eyes, nose and mouth.

Reduce stresses on your herd. Most horses you’ve known have likely already been exposed to an EHV and are carrying the latent form of the virus, which can be reactivated under stressful conditions, such as travel, crowding, poor health or disruption of their social groups. Of course some stressors are inevitable, but any steps you can take to keep your horses healthy, happy and vigorous will go a long way toward keeping herpesviruses, as well as most other pathogens, at bay.

This excerpt is from the article “A Field Guide to Herpesviruses” in EQUUS magazine’s October 2002 issue.




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